In many service provider communication networks, provider edge (PE) routers provide the interfaces between customer premises equipment (CPE) and the provider network. The PE routers, in turn, directly or indirectly interface with area border routers (ABRs) that define the interfaces between edge segments of the provider network containing the CPE and PE routers (which are also referred to as edge networks), and the core segment of the provider network (which is also referred to as the core network). The combination of a core network and its associated edge networks is referred to as a domain or an autonomous system (AS). Furthermore, a provider network may include multiple autonomous systems or domains that are interconnected via autonomous system boundary routers (ASBRs).
In an example provider network, the core network is implemented using multiprotocol label switching (MPLS) that employs label switched paths (LSPs) to create communication paths between label switch routers (LSRs). The LSRs can be used to implement the ABRs, the provider (P) routers in the core network that interconnect the ABRs, and also the PE routers and ASBRs mentioned above. LSPs utilize labels for path identification, with switching being distributed among LSRs via point-to-point and/or multipoint label distribution protocols, such as label distribution protocol (LDP) and multicast LDP (mLDP), resource reservation protocol-traffic engineering (RSVP-TE) and RSVP-TE point-to-multipoint (P2MP), etc. A point-to-point LSP implements a communication path (also referred to as a tunnel) to enable traffic to be forwarded from a head-end node (e.g., such as a head-end LSR, which may be implementing a head-end PE router) for delivery to a single tail-end node (e.g., such as a tail-end LSR, which may be implementing a tail-end PE router). A multipoint LSP implements a multipoint communication path or tunnel to enable traffic to be forwarded from, for example, a root node (e.g., such as a root LSR, which may be implementing a root PE router) for delivery to multiple leaf nodes (e.g., such as multiple leaf LSRs, which may be implementing multiple leaf PE routers). Ingress replication is another technique that can be used to forward traffic (e.g., via replication) from a root node for delivery to multiple leaf nodes.